Means for equalizing transmission over lines of different electrical characteristics



June 19, 1923.

1,459,005 G. K. THOMPSON MEANS FOR EQUALIZING TRANSM DIFFERENT ELECTRICAL ISSION OVER LINES OF CHARACTERISTI F11 ed Oct. 29 1918 J6 %Q 1229'. 6w

J5 17 J49 J9 INVENTOR. flaw 195m 2. m

A TTORNEY Patented June 19, 1923.

* UNITED STATES GEORGE K. THOMPSON, OF MAPLEWOOD. NEW JERSEY, ASSIGNOR TO AMERICAN 'IELE PHONE AND TELEGRAPH COMPANY, A CORPORATION-OF NEW YORK.

MEANS Fort EQUALIZIVENG TRnNsMissIoN OVER LINES or DIFFERENT "matriarc CHARACTERISTICS.

Application filed October 29, 1918. Serial No. 260,149.

To all whom it may concern Be it knownthat I, GEORGE K. THOMP- -soN, residin at Maplewood, in the county of Essex and tate of New Jersey, have 'invented. certain Improvements in Means for Equalizing Transmission Over Lines of Different Electrical. Characteristics, of which the following ,is a specification. f ,This invention relates to telephone systems [0' and more particularly to the provision of means whereby the transmission over tele phone lines of different electrical characteristics may be equalized or rendered more unl- .form.

Telephone lines have, in general, different electrical characteristics varying. with the length of the lines. For any particular type v of line construction which maybe employed the resistance, capacity,.inductance and leakage of the circuit increase withthe length.

These variations inthe electrical characteristics of the different subscribers lines in ,a telephone system introduce a number of variable efi'ects in the telephone service rendered from difierent'stations. For example, the different electrical characteristics result indifferent degrees of attenuation in the alternating telephone current passing over the subscribers lines and thus givelouder and more effective telephonic communication to. subscribers connected by means of'short lines than'to subscribers connected by means of long lines. As a result, a subscriber having a long line, when connected with any other transmission and it is one of the objects of this invention to provide means whereby this difficulty may be overcome, although other subscriber, does not receive as goodrtele vide all subscribers with the same gradeot and further objects of the invention will pear from the description hereinaftergiven.

The objects of'this invention may be secured by associating with each line a telephone transmitter whose resistance is adjusted in accordance with the electrical characteristics 'of the line. Where the transmission line is of high impedance, since the direct current supplied to the transmitter over the line is small, the transmitter should be ofhigh resistance so that for a given varia tion of the transmitter resistance a proportionately large variation of .thetotal resistance including that of the line will be produced, and consequently a greater transmission efliciency Will result. Where the line is of low impedance and the current supplied 'large, the transmitter resistance should be comparatively small, so that a given variation' in the transmitter resistance produces a relatively, small variation in the total resistance. Consequently the transmission efficiency under this condition may be made dition above mentioned.

'75 little if any greater than under thefirst coni In its more specific aspects the invention contemplates the provision of a transmitter having a resistance element of-the type disclosed inpatents to RLC. Browne No. 854025, 920424 and 920425, said resistance element having a plurality offixedelectrodes embedded in granular material, and a plunger movable with the transmitter diaphragm for varying the resistance of the granular material. By this arrangement a plurality ofpaths of difierent resistance may 1 be established through the resistance element in a direction parallel to ,the'transmitter diaphragm and, by variably connecting these paths the resistance of the transmitterrmay" be adjusted in accordance with the requirements of the line with which it is to be associated. i

Theinvention may now be fully under stood from the'following description when read in connection with the accompanying drawings in Which i I j Figure 1 is asectional view of a transmitter embodying the principles of the invention; I

Figures 2,22 3, 1, Band 5 are views of details of the resistance elementyand Figures 6, 6, 6 6, 6 and 6 are circuit diagrams showing a number of different ways in which the electrodes of the resistance element may be connected.

Referring to Figure 1 a telephone transmitter is shown comprising the usual front casing 1, back casing or shell 2, mouthpiece 3, supporting bridge 4: and diaphragm 5. Suitably mounted upon the supporting bridge 4 is a granular carbon resistance element 6 of the eneral type disclosed in the patents to R. This resistance element comprises a rectangular container 7 of non-conducting material in which the granular material is placed with a mica diaphragm 8 secured to the front face of the container. The mica diaphragm 8 carries a plunger comprising members 9 and 10 clamped upon either side thereof as shown in Figure 5, the member 9 being provided with a centrally located boss 11 projecting through the diaphragm 8 and the member 10 and suitably secured to the diaphragm 5. A plurality of fixed electrodes 12, 13, 14 and 15 are embedded in the granular material, and while these electrodes may have any desired spacing with reference to each other, they are preferably arranged as shown in Figures 1 and 6 so that the electrode 12 is somewhat distant from the other electrodes. The action of the plunger in response to movements of the diaphragm 5 varies the resistance of the granular material of the resistance element and thereby varies the resistance of the paths between the electrodes.

The electrodes may be interconnected in a number of different ways depending upon the electrical characteristics of the line with which the transmitter is to be associated. As shown in Figure 6 conductors extend from the electrodes 12, 13, 14 and 15 to terminals 16, 17, 18 and 19 respectively. By connecting one side of the line L to the ter minal 16 and connecting the other side to the terminals 17 18 and 19 which are strapped together, a low resistance connection is obtained suitable for a transmitter to be used in connection with a line of low 'impedance. By connecting one side of the line to terminal 16 and the other side of the line to the terminal 17 of the nearest electrode, a transmitter of somewhat greater resistanceis obtained as shown in Figure 6. By connecting the other side of the line to the terminal 18 of a still more distant electrode as shown in Figure 6 a transmitter of still higher resistance is obtained. By connecting the line to terminals 16 and 19 of the two most distant electrodes the Browne above referred to. 1

highest resistance transmitter possible with this arrangement is secured and this con nection is best adapted for lines of very high impedance. Still other adjustments of the resistance of the transmitter may be obtained by strapping together terminals 18 and 19 and connecting the line to'terminals 16 and the two strapped terminals, or by strapping together terminals 17 and 18 and connecting one side of the line to these terminals and the other side to the terminal 16.

It will be seen that by means of the arrangements above described a large number of combinations may be obtained, so that a considerable variation in the resistance of ing instruments on loops of different. length will receive substantially the same transmission. It will also be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated with- I out departing from the spirit of the invention as defined in the following claims.

lVhat is claimed is: 1. A telephone transmitter for usein connection with lines of different electrical characteristics, said transmitter including" a diaphragm and a resistance element, havinga plurality of fixed electrodes embedded in granular material and a non-conducting plunger movable with said diaphragm to vary the resistance of said granular ma-"' terial, and means for interconnecting said electrodes differently in accordance with the electrical characteristics of the lines with which the transmitter is to be used. I

2. A telephone transmitter for use in con granular material and a non-conductive plunger movable with said diaphragm to vary the resistance of said granular material, and means to establish circuits in -a Ill) direction parallel to said diaphragm between two or more of said electrodes depending upon the electrical characteristics of the line with which the transmitter is to be used.

In testimony whereof, I have signed my name to this specification this 3rd day of October, 1918.

GEORGE K. 'rHoMrsoN. 

